In general, inkjet printers include at least one printhead that ejects drops of liquid ink onto an image receiving surface to produce ink images on recording media. A phase change inkjet printer employs phase change inks that are in the solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. A mounted printhead ejects drops of the melted ink to form an ink image on an image receiving surface. The image receiving surface can be the surface of print media or an image receiving member, such as a rotating drum or endless belt. Ink images formed on an image receiving member are later transferred to print media. Once the ejected ink is onto the media or image receiving member, the ink droplets quickly solidify to form an image.
The media on which ink images are produced can be supplied in sheet or web form. A media sheet printer typically includes a supply drawer that houses a stack of media sheets. A feeder removes a sheet of media from the supply and directs the sheet along a feed path past a printhead so the printhead ejects ink directly onto the sheet. In offset sheet printers, a media sheet travels along the feed path to a nip formed between the rotating imaging member onto which the ink image was formed and a transfix roller. The pressure and heat in the nip transfer the ink image from the imaging member to the media. In a web printer, a continuous supply of media, typically provided in a media roll, is entrained onto rollers that are driven by motors. The motors and rollers pull the web from the supply roll through the printer to a take-up roll. As the media web passes through a print zone opposite the printhead or heads of the printer, the printheads eject ink onto the web. Along the feed path, tension bars or other rollers remove slack from the web so the web remains taut without breaking.
An inkjet printer conducts various maintenance operations to ensure that the ink ejectors in each printhead operate efficiently. A cleaning operation is one such maintenance operation. The cleaning process removes particles or other contaminants that may interfere with printing operations from the printhead and may unclog solidified ink or contaminants from inkjet ejectors. During a cleaning operation, the printheads purge ink through some or all of the ink ejectors in the printhead. The purged ink flows through the ejectors and down the front face of the printheads, where the ink drips into an ink receptacle. To control the flow of ink down the face of each printhead, some printheads include a drip bib. The drip bib has a shape that directs liquid ink toward the ink receptacle. The lower edge of the drip bib tapers to one or more channels or points where ink collects prior to dripping into the receptacle. In some printers, a wiper engages the front face of the printhead and wipes excess purged ink in a downward direction toward the drip bib to remove excess purged ink.
FIG. 4 depicts a prior art printhead assembly 400. The printhead assembly 400 includes a housing 404, printhead face or printhead face plate 408, inkjet nozzle plate 410, and a drip bib 412. The drip bib 412 includes an upper end 414 below the nozzle plate 410 and a lower edge that forms multiple tips 416A, 416B, 416C, and 416D. In alternative configurations, the drip bib 412 can include different configurations of the lower edge or liquid channels that direct purged ink toward a waste ink receptacle. During a maintenance operation, purged ink flows out of the inkjet nozzles in the inkjet nozzle plate 410 and flows down the printhead face 408 and drip bib 412 in direction 440 under the force of gravity. Most of the liquid ink concentrates near the tips 416A-416D of the drip bib and drips from the printhead assembly 400 into the waste ink receptacle. Some of the ink, however, can adhere to either the printhead face 408 or the drip bib 412 or both structures.
While the cleaning process removes most purged ink from the face of the printhead and the drip bib, small amounts of residual ink may accumulate on both the printhead face and the drip bib over time. These small amounts of ink can be produced by printing operations and by printhead maintenance operation. Ink that accumulates on the printhead face plate promotes “drooling” of ink through one or more inkjet nozzles due to capillary attraction between ink on the face of the printhead and ink within a pressure chamber in nearby inkjets. The drooled ink can form spurious marks on the image receiving surface and can interfere with the operation of inkjets in the printhead. Ink that adheres to the drip bib collects near a lower edge of the drip bib and can release from the drip bib after completion of the maintenance operation. In addition to forming spurious marks on the print medium, phase-change inks on drip bibs can cool and solidify prior to being released from the drip bib. The moving print media can carry the solidified ink past the printhead where the solidified ink can strike the printhead face with possibly adverse consequences to the printhead.
Existing printhead faces and drip bibs are often coated with a low surface energy material, such as polytetrafluoroethylene, which is sold commercially as Teflon®. The low surface energy material is also referred to as an “anti-wetting” material that resists the adhesion of liquid ink to the printhead or the drip bib. The low surface energy material is applied during the manufacture of the printhead face and drip bib. After prolonged use in a printer, however, the low surface energy coating can gradually wear away. For example, repeated contact with the print medium during operation can erode Teflon from the printhead face and the drip bib. Additionally, repeated contact with wiper blades and other printhead maintenance unit components can erode the low surface energy material. Over time, the printhead and drip bib may begin to accumulate larger amounts of excess ink, which can artificially shorten the operational lifetime of the printhead.